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import { Operator } from '../Operator';
import { Observable } from '../Observable';
import { Subscriber } from '../Subscriber';
import { MonoTypeOperatorFunction, TeardownLogic } from '../types';
/**
* Emits values emitted by the source Observable so long as each value satisfies
* the given `predicate`, and then completes as soon as this `predicate` is not
* satisfied.
*
* <span class="informal">Takes values from the source only while they pass the
* condition given. When the first value does not satisfy, it completes.</span>
*
* 
*
* `takeWhile` subscribes and begins mirroring the source Observable. Each value
* emitted on the source is given to the `predicate` function which returns a
* boolean, representing a condition to be satisfied by the source values. The
* output Observable emits the source values until such time as the `predicate`
* returns false, at which point `takeWhile` stops mirroring the source
* Observable and completes the output Observable.
*
* ## Example
* Emit click events only while the clientX property is greater than 200
* ```javascript
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(takeWhile(ev => ev.clientX > 200));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link take}
* @see {@link takeLast}
* @see {@link takeUntil}
* @see {@link skip}
*
* @param {function(value: T, index: number): boolean} predicate A function that
* evaluates a value emitted by the source Observable and returns a boolean.
* Also takes the (zero-based) index as the second argument.
* @return {Observable<T>} An Observable that emits the values from the source
* Observable so long as each value satisfies the condition defined by the
* `predicate`, then completes.
* @method takeWhile
* @owner Observable
*/
export function takeWhile<T>(predicate: (value: T, index: number) => boolean): MonoTypeOperatorFunction<T> {
return (source: Observable<T>) => source.lift(new TakeWhileOperator(predicate));
}
class TakeWhileOperator<T> implements Operator<T, T> {
constructor(private predicate: (value: T, index: number) => boolean) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new TakeWhileSubscriber(subscriber, this.predicate));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class TakeWhileSubscriber<T> extends Subscriber<T> {
private index: number = 0;
constructor(destination: Subscriber<T>,
private predicate: (value: T, index: number) => boolean) {
super(destination);
}
protected _next(value: T): void {
const destination = this.destination;
let result: boolean;
try {
result = this.predicate(value, this.index++);
} catch (err) {
destination.error(err);
return;
}
this.nextOrComplete(value, result);
}
private nextOrComplete(value: T, predicateResult: boolean): void {
const destination = this.destination;
if (Boolean(predicateResult)) {
destination.next(value);
} else {
destination.complete();
}
}
}
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